I need to wire two applications so that one reacts when another is selected.

I need a calendar view (populated in one application) to update when a person is selected from a list (based from another application).

I have been trying to do this for absolutely ages and have hit a brick wall as the existing knowledge base is pretty poor. I don't understand how to compose the action required to do this, or how to use the WDSL system to wire the two, which i will be linking using the UNID of the person.